I can tell you how they were made but I don't remember the name of the process.
It is similar to a hologram .... but holograms ar 3D.
In essence, there are very, very fine "V" ridges on the print medium ..... and 1 of the images is printed on the "left" side of the "V" ..... and the other image is printed on the "right" side of the "V".
Thus, if you are looking from the "left" side of center you will see 1 image. And looking from the "right" side of center you will see the 2nd image.
There were a lot of "novelty" items (like key-chain fobs, etc) in the 70's (I think) that had those "kinda" images on them.